Photodetecting circuit, optical receiver, and photocurrent measurement method for photo detector

Abstract

The present invention is a photodetecting circuit comprising a plurality of operational amplifiers provided so as to correspond to respective photo detectors disposed on a common semiconductor substrate, each operational amplifier having an inverting input terminal connected to a cathode of the photo detector and a non-inverting input terminal supplied with a voltage to be applied to the photo detector; a plurality of resistances connected between output terminals and inverting input terminals of the respective operational amplifiers; and a terminal, disposed on at least the inverting input terminal side in both ends of the resistance, for connecting with a meter for measuring a photocurrent of the photo detector.

What is claimed is: 
     
         1 . A photodetecting circuit comprising:
 a plurality of operational amplifiers provided so as to correspond to respective photo detectors disposed on a common semiconductor substrate, each operational amplifier having an inverting input terminal connected to a cathode of the photo detector and a non-inverting input terminal supplied with a voltage to be applied to the photo detector;   a plurality of resistances connected between output terminals and inverting input terminals of the respective operational amplifiers; and   a terminal, disposed on at least the inverting input terminal side in both ends of the resistance, for connecting with a meter for measuring a photocurrent of the photo detector.   
     
     
         2 . A photodetecting circuit according to  claim 1 , wherein the terminal for connecting with the meter for measuring the photocurrent of the photo detector is disposed on at least the inverting input terminal side in both ends of each of the plurality of resistances. 
     
     
         3 . A photodetecting circuit according to  claim 1 , wherein phases of light received by the plurality of photo detectors are shifted from each other. 
     
     
         4 . A photodetecting circuit according to  claim 1 , wherein the voltage in common is supplied to the respective non-inverting input terminals of the plurality of operational amplifiers. 
     
     
         5 . An optical receiver comprising the photodetecting circuit according to  claim 1 ; and
 the plurality of photo detectors having cathodes connected to the respective inverting input terminals of the plurality of operational amplifiers.   
     
     
         6 . An optical receiver according to  claim 5 , further comprising a 90° hybrid coupler for receiving signal light and local oscillation light and emitting interference light formed by the signal light and local oscillation light interfering with each other;
 wherein the photo detectors receive the interference light emitted from the 90° hybrid coupler. 
 
     
     
         7 . An optical receiver according to  claim 5 , further comprising a transimpedance amplifier connected to an anode of the photo detector. 
     
     
         8 . An optical receiver according to  claim 7 , wherein the transimpedance amplifier comprises two input terminals; and
 wherein the two input terminals receive respective photocurrents issued from two of the photo detectors.   
     
     
         9 . A photocurrent measurement method for a photo detector, the method comprising the steps of:
 connecting a plurality of operational amplifiers to respective photo detectors disposed on a common semiconductor substrate, the operational amplifiers having inverting input terminals connected to cathodes of the photo detectors and non-inverting input terminals supplied with a voltage to be applied to the photo detectors; and   measuring currents flowing through connection lines connecting the inverting input terminals and output terminals of the respective operational amplifiers in a state where an optical signal is fed to the photo detectors, so as to determine photocurrents of the photo detectors.